From: Public Services and Procurement Canada
Aerobic composting is an ex situ remediation technology that can be carried out on or off-site, where microorganisms present in the soil are used to degrade contaminants and use them as an energy source. This technology operates under aerobic conditions and generates high temperatures (between 54 °C and 65 °C).
Aerobic composting consists in mixing contaminated soils with structuring agents (wood chips, hay and/or manure), organic amendments and/or plant residues. Specific microorganisms can also be added to stimulate the biodegradation of contaminants.
There are three main methods for aerobic composting:
Sources:
The implementation of aerobic composting may include:
On-site storage may include amendments, nutrients, fuel, lubricants, and other site materials required for treatment, operation of machinery, and equipment needed to implement the process.
Temporary piles of contaminated soil awaiting treatment or transport off-site may also be found on the site.
Sites with seepage water in excavation areas and/or runoff can store it in tanks if it is contaminated. They can also treat it on site, which requires storage of materials for the operation of the water treatment system.
All contaminated soil is normally excavated. Therefore, there is minimal residue associated with this technology. The waste on site is typical of a construction site.
Dust may be emitted from excavations, soil treatment areas, or soil spread on the ground by equipment wheels or tracks. Vapour effluents may be emitted from the volatilization of contaminants from excavation walls or temporary piles and/or excavation water if dewatering is required. These effluents may need to be treated.
Natural biodegradation, particularly of hydrocarbons, can also produce vapour emissions of non-contaminant products. These products may include carbon dioxide, ammonia, methane and/or hydrogen sulphide.
The technology applies to organic compounds that can be degraded under aerobic conditions.
Applicable for the treatment of soils that have conditions favourable to biodegradation: the soil temperature should generally be between 54 °C and 65 °C, the pH between 6 and 8, and the humidity between 50% and 80%.
Notes:
Aerobic composting may require months or a few years to treat contaminated soils. Less volatile and more recalcitrant compounds may require up to two years of treatment. Easily degradable compounds can be treated in a few weeks.
Contaminated soils are excavated and will only be reused on site if they meet the environmental and geotechnical criteria allowed for the site. In this sense, little to no long-term consideration exists at the treated sites following backfilling and when the equipment and facilities have been dismantled.
Aerobic biodegradation of organic contaminants does not usually generate toxic by-products or metabolites. It generates products such as carbon dioxide and water.
However, some recalcitrant compounds, such as explosives, can generate toxic metabolites during composting.
Complementary technologies can be combined with aerobic composting to improve its efficiency. These technologies include:
The addition of hot air to increase the soil temperature (54 °C to 65 °C) to stimulate bacterial growth and biodegradation.
The following links provide application examples:
The turned windrow method (compost is placed in long piles and turned periodically using machinery) appears to be the most cost-effective type of aerobic composting. A high level of treatment, 99% or more reduction in contaminant levels, has been observed in the past.
Composed by : Magalie Turgeon, National Research Council
Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada
Updated Date : March 1, 2015
Latest update provided by : Nathalie Arel ing., M.Sc., Frédéric Gagnon CPI., Sylvain Hains ing., M.Sc., Golder Associates Ltd.
Updated Date : March 30, 2022
